gs_usb, interface: fix bug on second .start() by repeating in shutdown()

v2:
updates as per review #1790 (review) by @zariiii9003

Author: BenGardiner

can/interfaces/gs_usb.py

@@ -33,18 +33,24 @@ def __init__(
         :param can_filters: not supported
         :param bitrate: CAN network bandwidth (bits/s)
         """
+        self._is_shutdown = False
         if (index is not None) and ((bus or address) is not None):
             raise CanInitializationError(
                 "index and bus/address cannot be used simultaneously"
             )
 
+        if index is None and address is None and bus is None:
+            index = channel
+
+        self._index = None
         if index is not None:
             devs = GsUsb.scan()
             if len(devs) <= index:
                 raise CanInitializationError(
                     f"Cannot find device {index}. Devices found: {len(devs)}"
                 )
             gs_usb = devs[index]
+            self._index = index
         else:
             gs_usb = GsUsb.find(bus=bus, address=address)
             if not gs_usb:
@@ -68,6 +74,7 @@ def __init__(
             brp=bit_timing.brp,
         )
         self.gs_usb.start()
+        self._bitrate = bitrate
 
         super().__init__(
             channel=channel,
@@ -154,5 +161,21 @@ def _recv_internal(
         return msg, False
 
     def shutdown(self):
+        if self._is_shutdown:
+            return
+
         super().shutdown()
         self.gs_usb.stop()
+        if self._index is not None:
+            # Avoid errors on subsequent __init() by repeating the .scan() and .start() that would otherwise fail
+            # the next time the device is opened in __init__()
+            devs = GsUsb.scan()
+            if self._index < len(devs):
+                gs_usb = devs[self._index]
+                try:
+                    gs_usb.set_bitrate(self._bitrate)
+                    gs_usb.start()
+                    gs_usb.stop()
+                except usb.core.USBError:
+                    pass
+        self._is_shutdown = True